Hot Source Cleaning System

ABSTRACT

There is an apparatus for cleaning a substrate mounted on a moveable platen. In an example embodiment, the apparatus comprises a first chamber, the first chamber has solvent-dispensing nozzles; the solvent-dispensing nozzles wet the substrate surface with a solvent as the platen transports the substrate. The platen moves in a predetermined direction and at a predetermined scan velocity as it transports the substrate into a process chamber. The process chamber has a hot source at a predetermined height from the substrate surface; it provides heat energy directed toward the substrate surface, the heat energy evaporates the solvent dispensed on the substrate surface; the solvent evaporation removes particulates from the substrate surface, as the platen transports the substrate from the first chamber into the process chamber. Substrates cleaned may include precision photo-masks, or wafers.

The present invention relates the processing semiconductors. Moreparticularly, the present invention relates to the removal of sub-micronparticles during the cleaning of a substrate.

The electronics industry continues to rely upon advances insemiconductor technology to realized higher-function devices in morecompact areas. For many applications, realizing higher-functioningdevices requires integrating a large number of electronic devices into asingle silicon wafer. As the number of electronic devices per area ofthe silicon wafer increases, the manufacturing process becomes moredifficult.

Many varieties of semiconductor devices are manufactured having variousapplications in numerous disciplines. Such silicon-based semiconductordevices often include metal-oxide-semiconductor field-effect transistors(MOSFET), such as p-channel MOS (PMOS), n-channel MOS (NMOS) andcomplementary MOS (CMOS) transistors, bipolar transistors, BiCMOStransistors. Such MOSFET devices include an insulating material betweena conductive gate and silicon-like substrate; therefore, these devicesare generally referred to as IGFETs (insulated-gate FET).

Each of these semiconductor devices generally includes a semiconductorsubstrate on which a number of active devices are formed. The particularstructure of a given active device can vary between device types. Forexample, in MOS transistors, an active device generally includes sourceand drain regions and a gate electrode that modulates current betweenthe source and the drain regions. In bipolar transistors, an activedevice generally includes emitter and collector regions and a baseelectrode to control operation of the transistor.

Furthermore, such devices may be digital or analog devices produced in anumber of wafer fabrication processes, for example, CMOS, BiCMOS,Bipolar, etc. The substrates may be silicon, gallium arsenide (GaAs) orother substrate suitable for building microelectronic circuits thereon.

One important step in the manufacturing of such devices is the formationof devices, or portions thereof, using photolithography and etchingprocesses. In photolithography, a wafer substrate is coated with alight-sensitive material called photo-resist. Next, the wafer is exposedto light; the light striking the wafer is passed through a mask plate.This mask plate defines the desired features to be printed on thesubstrate. After exposure, the resist-coated wafer substrate isdeveloped. The desired features as defined on the mask are retained onthe photo resist-coated substrate. Unexposed areas of resist are washedaway with a developer. The wafer having the desired features defined issubjected to etching. Depending upon the production process, the etchingmay either be a wet etch, in which liquid chemicals are used to removewafer material or a dry etch, in which wafer material is subjected to aradio frequency (RF) induced plasma.

Often desired features have particular regions in which the finalprinted and etched regions have to be accurately reproduced over time.These are referred to as critical dimensions (CDs). As device geometryapproaches the sub-micron realm, wafer fabrication becomes more relianton maintaining consistent CDs over normal process variations. The activedevice dimensions as designed and replicated on the photo mask and thoseactually rendered on the wafer substrate have to be repeatable andcontrollable. In many situations, the process attempts to maintain thefinal CDs equal to the masking CDs.

As the CDs are trending smaller in the advancing of the technology, theadequate cleaning of the mask plates becomes critical. Any particlespresent on the surface of the mask plate may be imaged as an undesirablefeature on the silicon substrate, resulting in a defect. Too manydefects cause device failure and lower yield. The size of such particlesis trending into the submicron realm, about 100 nm or less.

Removal of sub 100 nm particles from a surface is a challenging subjectof today's surface preparation research. The surface-particleinteractions depend on detail surface structure of the materialsinvolved and generally are size independent. However, the energytransfer efficiency to a particle on a surface strongly depends on thesize of the particle on the surface. To remove a particle from a surfaceone firstly, has to overcome the adhesive forces between the particleand the surface and secondly, transport the particle far from thesurface in a safe distance over which the particle is not re-depositedon the surface.

Next generation semiconductor technology uses reflective optics, whichrequires extremely flat surfaces with an average roughness of 1.5Angstrom RMS. Hence, the conventional wet cleaning techniques that usethe under etching of a particle to remove it from the surface no longerare applicable.

For sub-100 nm particle removal, one should use a physical mechanism inaddition to chemical techniques to separate the particle from thesurface. There are different techniques that offer some kind of physicalinteractions between an energy source and the particle.

Among them is the laser cleaning technique, which uses laser interactionwith the particle to remove it from the surface. Liquid-assisted lasercleaning is a technique that uses sudden evaporation of a liquid (water)on the surface under exposure to laser pulses. Laser cleaning poses arisk of damage to the substrate. This is due to power dissipation in aconcentrated area in the substrate. Some laser cleaning techniqueshortcomings include that high-density power is focused at a point andthe power transfer to the substrate is not readily controllable. Furtherinformation may be found in U.S. Pat. No. 6,494,217 (issued Dec. 17,2002) of Thompson et al. titled, “Laser Cleaning Process forSemiconductor Material and the Like,” incorporated by reference in itsentirety.

There exists a need for a technique that can overcome the challengesencountered with liquid-assisted laser cleaning.

The present invention has been found useful in the cleaning ofsubstrates, such as photo masks. A hot source is adapted to vaporize thewater (nano) droplets present on the surface. The sudden evaporation ofthe water molecules at the surface will lead to lateral energy transferto the undesirable particles that have adhered to the surface. Thismomentum can separate these particles from the surface.

In an example embodiment according to the present invention, there is anapparatus for cleaning a substrate mounted on a moveable platen. Theapparatus comprises a first chamber, the first chamber havingsolvent-dispensing nozzles. The solvent-dispensing nozzles wet thesubstrate surface with a solvent as the platen transports the substrate.The platen moves in a predetermined direction and at a predeterminedscan velocity. The platen transports the substrate from the firstchamber into a process chamber, having a hot source at a predeterminedheight from the substrate surface, providing heat energy directed towardthe substrate surface, the heat energy evaporating the solvent dispensedon the substrate surface, the solvent evaporation removing particulatesfrom the substrate surface, as the platen transports the substrate fromthe first chamber into the process chamber. A feature of thisembodiment, further comprises a second chamber. The second chamber hassolvent-dispensing nozzles re-wetting the substrate surface with thesolvent, as the platen transports the substrate from the process chamberinto the second chamber. The solvent-dispensing nozzles may dispense avariety of solvents depending upon the substrate to be cleaned. Solventsmay be selected from but not limited to, water, detergent, an organicsolvent, liquid carbon dioxide, and liquid nitrogen. Another feature ofthis embodiment further comprises a substrate heater to raise thetemperature of the substrate to predetermined temperature below anevaporation temperature of the solvent in the process chamber.

In another example embodiment according to the present invention, thereis an apparatus for cleaning a substrate mounted on a moveable platen.The apparatus comprises a first chamber, the first chamber havingsolvent-dispensing nozzles. The solvent-dispensing nozzles wet thesubstrate surface with a solvent as the platen transports the substrate.The platen moves in a predetermined direction and at a predeterminedscan velocity. The platen transports the substrate from the firstchamber into a process chamber, having a hot source at a predeterminedheight from the substrate surface, providing heat energy directed towardthe substrate surface, the heat energy evaporating the solvent dispensedon the substrate surface, the solvent evaporation removing particulatesfrom the substrate surface, as the platen transports the substrate fromthe first chamber into the process chamber. There is a second chamberthat has solvent-dispensing nozzles re-wetting the substrate surfacewith the solvent, as the platen transports the substrate from theprocess chamber into the second chamber.

In yet another example embodiment, there is a system for cleaning asubstrate surface. The system comprises, a means for placing thesubstrate in a first chamber. In the first chamber, there are means fordepositing atomized water droplets on the substrate surface. Afterdepositing the atomized water droplets, there are means for transportingthe substrate to a process chamber. Within the process chamber, thereare means for exposing the substrate to a hot source; the hot sourceevaporates the water deposited on the substrate surface, the waterevaporation removing particulates form the substrate surface. Means forcarrying the particulates away from the substrate surface prevent there-deposition of the particulates on the substrate surface. Additionalfeatures of the embodiment further comprise, means for making adetermination of whether the substrate surface is sufficiently clean. Ifthe determination shows the substrate surface is not sufficiently clean,there are means for transporting the substrate to a second chamberdepositing atomized water droplets on the substrate surface and meansfor transporting the substrate back to the process chamber to re-exposethe substrate surface to the hot source. If the determination shows thesubstrate surface is sufficiently clean, there is a means for showing anend-of-clean indication.

In yet another example embodiment, there is a method for cleaning asubstrate. The method comprises, placing the substrate in a firstchamber and depositing atomized water droplets on the substrate surface.The substrate is transported to a process chamber and the substrate isexposed to a hot source, the hot source evaporates the water depositedon the substrate surface, the wafer evaporation removing particulatesfrom the substrate surface and carrying the particulates away from thesubstrate surface. The substrate is transported to a second chamber andatomized water droplets are deposited on the substrate surface.Additional features of the method further comprise, making adetermination of whether the substrate surface is clean and if clean,moving the substrate to a dryer. If the substrate surface is not clean,the substrate is transported back to the process chamber, and re-exposedto the hot source, the hot source evaporating the water deposited on thesubstrate surface. The water evaporation removes particulates from thesubstrate surface and carries the particulates away from the substratesurface. The substrate is transported back to the first chamber or thesecond chamber and atomized water droplets are re-deposited on thesubstrate surface. The determination of whether the substrate is cleanis repeated. The above summaries of the present invention are notintended to represent each disclosed embodiment, or every aspect, of thepresent invention. Other aspects and example embodiments are provided inthe figures and the detailed description that follow.

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a side view of an apparatus for removing particles from asubstrate according to an embodiment of the present invention; and

FIG. 2 is a top view and close-up side view of the heat source of theapparatus shown in FIG. 1; and

FIG. 3 is a flowchart of the particle removal process a substrateundergoes according to an embodiment of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims

The present invention has been found useful removing sub 100 nmparticles from substrates, in particular precision glass substrates suchas those used in photo masks. It is important to render those featureson the photo mask that are desired, to the silicon substrate.Contaminants such as dust particles, such as those which a photo maskmay encounter in normal use and handling or chrome which had not etchedin the photo mask's manufacture, results in the printing undesiredfeatures on the silicon substrate. In removing the sub-100 nm particles,the forces the bind the particles to the substrate's surface have to beovercome.

In an example embodiment according to the present invention, there is ahot source cleaning system (HSCS). Refer to FIG. 1. The HSCS includes afirst (pre-process) chamber 20 and a second (post process) chamber 40,two cold traps (34, 36), and a process chamber 30 having a hot source35. To isolate the first chamber 20 and second chamber 40 from the heatof process chamber 30, an insulator material 25 is included.

Substrate 5 enters in the pre-process chamber 20. The substrate 5 iscarried by a platen (not illustrated); the platen transports thesubstrate between the first chamber 20, process chamber 30 and secondchamber 40. The pre-process chamber 20 has nozzles 25 that produce verysmall water vapor droplets 7 (i.e., an atomizer). The water droplets aredeposited on the substrate surface 5. The shape of the droplet depends(i.e. contact angle) on the surface properties whether the surface ishydrophilic or hydrophobic. The substrate 5 then moved under a hot steamsource 30 that blows hot steam on the substrate surface 5. As the steamtemperature may be much more than the boiling temperature of water, thehot steam instantly vaporizes the water droplets 7 along the length ofthe substrate. This sudden evaporation releases enough energy on thesubstrate surface 5 and transfers momentum to the particles that adhereto the substrate surface 5. These particles 38 will be dislodged fromthe substrate surface 5 and some of them leave the surface with hotvapor. With a vacuum chuck 32 and a carrier gas 33, the dislodgedparticles are taken away from the substrate. The carrier gas may benitrogen (N₂) or argon (Ar) carbon dioxide (CO₂) or other suitable inertgas. Furthermore, cold traps 34 a, 34 b adjacent to the particlescollect any water vapor that may redeposit onto the substrate 5. Coolant31 circulates through the cold traps 34 a, 34 b to maintain a steadycool temperature.

The substrate 5 is transferred to the second (post-process) chamber 40from the process chamber 30. Within the second chamber 40, waterdroplets are again deposited onto the substrate through nozzles 45. Thesubstrate 5 is moved back to the hot source 35 in the process chamber 30for additional particle removal. If more particle removal is desired,the substrate 5 is transferred back to the first chamber 20 whereadditional water droplets are deposited. Transfer between the firstchamber 20 through the process chamber 30 and second chamber 40 may berepeated until the substrate is sufficiently clean per predeterminedprocess requirements.

Having been sufficiently clean, the wet substrate 5 is sent to an IPAdryer (e.g., isopropyl alcohol dryer). After drying, the substrate maybe placed in contamination resistant packaging for later processing oruse.

In another embodiment according to the present invention, the dryingapparatus may use heaters 10 (e.g. lamp, resistive) to heat thesubstrate 5. The heater slowly raises the temperature to a value about10° C. to 20° C. below evaporation temperature of water. As thetemperature of substrate 5 is more than surroundings, thermo-phoreticforces reduce particle re-deposition on the surface. In addition, lessenergy to evaporate a water droplet on the surface is required.

In yet another embodiment, in lieu of hot steam, the hot source 30 canradiate dry heat that may be directed to the substrate 5. Refer to FIG.2. The figure shows the detail mechanism of heat focusing and theinvolved parameters. Hot source 30 radiates heat that passes through arectangular aperture with width (G). The length (L) of the aperture ispredetermined by the width of the substrate 5 processed through theapparatus. The scattering of the heat from the aperture edge can be usedas a Fresnel diffraction lens. Total energy transfer to substratesurface 5 can be controlled by the gap distance G. The additional heatwill be adsorbed by the upper surface of the cold trap.

The substrate scan velocity (V) can be used to control the total energytransferred to the unit area of the substrate surface. Therefore, bycontrolling the total radiation power of the source, gap distance G andsubstrate scan velocity V, one can get optimum energy to instantlyevaporate the water droplet on the surface and yet do not heat thesubstrate that may cause surface deformation defects.

In another example embodiment according to the present invention, thecleaning apparatus may be set up to go through the pre-programmedprocedure. Refer to FIG. 3. A substrate undergoes a cleaning process200. The substrate is placed in a first process chamber. Atomized waterdroplets are deposited onto the substrate 210. The substrate is moved tothe hot steam source 215. Particulates are removed from the substrate.The substrate is moved to a second process chamber 220. Based onempirical evidence and other appropriate analysis, there is a standardof cleanliness required. The cleaning apparatus is programmed todetermine whether the substrate is clean 125. If sufficiently clean 125,the cleaned substrate is moved to a dryer 245. If not, the substrate hasadditional atomize water droplets deposited thereon 225. The substrateis again moved to the hot steam source 230 and cleaned further. Aftercleaning, the substrate is moved back to the first process chamber 235.If the substrate is sufficiently clean 140, the cleaned substrate ismoved to the dryer. If the substrate is not clean, the process continueswith additional atomized water droplets applied to the substrate 210.The process continues until the substrate is sufficiently clean. For aquartz mask substrate temperature can be as high as 1000° C. However, itis not desirable to expose a precision flat mask to such a hightemperature. During cleaning it is preferred, to keep a temperature ofthe mask plate below a 100° C. An example wet clean process can heat upthe plates to about 110° C.

In drying the mask substrate, in an example process may be to have amask holder under post process chamber adapted to spin-dry the masksubstrate. The drying process begins by the spinning plates undernozzles while ultra-pure water is sprayed on the mask surface. In thenext step, water spray will stop while spinning continues. Spinningalone dries the plates. Furthermore, IPA may be mixed in after waterspray to reduce surface tension to facilitate water removal. Spin-dryingis well known in the art.

Through experimentation, the number of cycles needed to clean thesubstrate may be determined. Defect inspection tools would be needed toscan submicron particles remaining after cleaning. In an examplemanufacturing line, an inspection tool would be proximity to thecleaning apparatus so that the substrate may be inspected after a seriesof cleaning cycles.

In this technique, there are a number of parameters to adjust the powertransferred to the substrate (G, h, v, Total power, Cooling rate). Asmost of these parameters technically can be easily controlled, a morecontrolled vertical heat profile may be achieved. These parameters maythen be programmed into the equipment having a computer-controlledinterface. The transmitted energy (R_(E)) is proportional with inverseof square of distance. R_(E)∝1/h² and the inverse of gap distanceR_(E)∝1/g. Scan velocity determines energy radiated to the units ofsurface area. The faster the scan velocity, the larger the exposed areaof the mask surface and therefore less energy transferred to the unitsof surface. A rough estimate is R_(E)∝1/ν_(scan). Specific parametersand coefficients would be derived from empirical data collected from agiven apparatus set up to clean a particular substrate type. Throughprocess development, the optimum process is derived.

In another example process according to the present invention, othersolvents in addition to water may be used. These may include, but arenot necessarily limited to, organic solvents, detergents, surfactants,liquid nitrogen, liquid CO₂. The type or condition of the substrate tobe cleaned would govern the solvent selection. For example, one commoncase is functionalized water in which ozone (O₃), hydrogen (H₂), CO₂ andso on are dissolved in the water. Surfactants are also often is added towater to increase the effectiveness of the cleaning.

Although the afore-mentioned examples involved mask substrates, theinvention may be applied to wafer substrates, mask substrates, or otherprecision substrates requiring the removal of microscopic particles.Furthermore, the invention may be used for both patterned andun-patterned substrates.

Numerous other embodiments of the invention will be apparent to personsskilled in the art without departing from the spirit and scope of theinvention as defined in the appended claims.

1. An apparatus for cleaning a substrate mounted on a moveable platen,the apparatus comprising: a first chamber the first chamber havingsolvent-dispensing nozzles the solvent-dispensing nozzles wetting thesubstrate surface with a solvent as the platen transports the substrate,the platen moving in a predetermined direction and at a predeterminedscan velocity; and a process chamber, the process chamber having a hotsource at a predetermined height from the substrate surface, providingheat energy directed toward the substrate surface, the heat energyevaporating the solvent dispensed on the substrate surface, the solventevaporation removing particulates from the substrate surface, as theplaten transports the substrate from the first chamber into the processchamber.
 2. The apparatus as recited in claim 1, further comprising, asecond chamber the second chamber having solvent-dispensing nozzles thesolvent-dispensing nozzles re-wetting the substrate surface with thesolvent, as the platen transports the substrate from the process chamberinto the second chamber.
 3. The apparatus as recited in claim 1, whereinthe solvent-dispensing nozzles dispense a solvent selected from at leastone the following: water, detergent, an organic solvent, liquid carbondioxide, liquid nitrogen.
 4. The apparatus as recited in claim 1, theapparatus further comprising, a substrate heater, the substrate heaterraising the temperature of the substrate to a redetermined temperaturebelow an evaporation temperature of the solvent in the process chamber.5. The apparatus as recited in claim 1, wherein the heat energy includesat least one of the following: dry heat, hot steam.
 6. The apparatus asrecited in claim 1, wherein the process chamber further includes, a coldtrap a vacuum chuck built into the cold trap carrier gas orifices in thevicinity of the hot source wherein a carrier gas emanates from theorifices, removing the particulates carried by the solvent evaporatedfrom the substrate surface with the hot source the vacuum chuckcapturing the particulates removed from the substrate surface.
 7. Theapparatus as recited in claim 6, wherein the carrier gas includes atleast one of the following: nitrogen, argon, carbon dioxide.
 8. Theapparatus as recited in claim 6, wherein the hot source furtherincludes, an aperture of a pre-determined gap distance (g) and length,the length of the aperture defined by the width of the substratetransported on the platen.
 9. The apparatus as recited in claim 8,wherein energy transmitted to the substrate surface is a function ofpower of the hot source, the predetermined height (h) of the hot sourcefrom the substrate surface, the predetermined gap distance (g), and thepre-determined scan velocity (v).
 10. The apparatus as recited in claim9, wherein the energy transmitted to the substrate surface is adjustedto instantly evaporate a water droplet on the substrate surface withoutheating the substrate surface to a temperature sufficient to causesurface deformation.
 11. The apparatus as recited in claim 9, furthercomprising, a scanner to determine a degree of cleanliness of thesubstrate, the scanner providing the apparatus an end of cleaningindication.
 12. An apparatus for cleaning a substrate mounted on amoveable platen, the apparatus comprising: a first chamber the firstchamber having water-dispensing nozzles the water-dispensing nozzleswetting the substrate surface as the platen transports the substrate,the platen moving in a predetermined direction and at a predeterminedscan velocity; a process chamber, the process chamber having a hotsource at a predetermined height from the substrate surface, providingheat energy directed toward the substrate surface, the heat energyevaporating the water dispensed on the substrate surface, the waterevaporation removing particulates from the substrate surface, as theplaten transports the substrate from the first chamber into the processchamber; and a second chamber the second chamber having water-dispensingnozzles, the water-dispensing nozzles re-wetting the substrate surface,as the platen transports the substrate from the process chamber into thesecond chamber.
 13. The apparatus as recited in claim 12, wherein theprocess chamber further includes, a cold trap a vacuum chuck built intothe cold trap carrier gas orifices in the vicinity of the hot sourcewherein a carrier gas emanates from the orifices, removing theparticulates carried by the solvent evaporated from the substratesurface with the hot source the vacuum chuck capturing the particulatesremoved from the substrate surface.
 14. System for cleaning a substratesurface, the system comprising, means for placing the substrate in afirst chamber means for depositing atomized water droplets on thesubstrate surface means for transporting the substrate to a processchamber; means for exposing the substrate to a hot source, the hotsource evaporating the water deposited on the substrate surface thewater evaporation removing particulates from the substrate surface; andmeans for carrying the particulates away from the substrate surface,thereby preventing re-depositing of the particulates on the substratesurface.
 15. The system as recited in claim 14, further comprising,means for making a determination of whether the substrate surface issufficiently clean; if the determination shows the substrate surface isnot clean, means for transporting the substrate to a second chamberdepositing atomized water droplets on the substrate surface; means fortransporting the substrate back to the process chamber and re-exposingthe substrate surface to the hot source; and if the determination showsthe substrate surface is clean, means for showing an end-of-cleanindication.
 16. A method for cleaning a substrate, the methodcomprising: a) placing the substrate in a first chamber and depositingatomized water droplets on the substrate surface b) transporting thesubstrate to a process chamber and exposing the substrate to a hotsource, the hot source, the hot source evaporating the water depositedon the substrate surface, the water evaporation removing particulatesfrom the substrate surface, and carrying the particulates away from thesubstrate surface; and c) transporting the substrate to a second chamberdepositing atomized water droplets on the substrate surface.
 17. Themethod as recited in claim 16, further comprising, d) making adetermination of whether the substrate surface is clean if clean, movingthe substrate to a dryer if not clean, e) transporting the substrateback to the process chamber and re-exposing the substrate to a hotsource, the hot source, the hot source evaporating the water depositedon the substrate surface, the water evaporation removing particulatesfrom the substrate surface, and carrying the particulates away from thesubstrate surface; f) transporting the substrate back to the firstchamber or the second chamber re-depositing atomized water droplets onthe substrate and g) repeating step d).
 18. The method as recited inclaim 17, wherein the hot source provides energy from at least one ofthe following: dry heat, hot steam.